The present invention relates generally to centrifugal separation of liquids and more particularly to an apparatus for automatically separating the serum, or plasma, from a whole blood sample for subsequent biochemical analysis.
Specific reference should be made to the following U.S. Pat. Nos. 3,049,889; 3,623,658; 1,534,604; and 736,976. Reference may also be made to the following U.S. Pat. Nos. 3,737,096; 3,722,790; 3,706,413; 3,635,394; 3,586,484; 3,439,871; 3,333,765; 3,235,173; 3,228,595; 3,211,368; 3,193,358; 3,190,547; 3,161,593; 3,151,073; 3,129,175; 2,948,462; 2,940,662; 2,906,453; 2,906,452; 2,906,451; 2,906,450; 2,822,315; 2,822,127; 2,822,126; 1,824,723; 621,706; 436,419; 360,342 and 241,172.
The modern medical research and diagnostic techniques in use today commonly rely on the analysis of blood samples. Whole blood, however, comprises a variety of immiscible components (e.g., the red cells, the white cells and the platelets) suspended in a colloidal serum, or plasma. Often, however, the analysis must be performed solely on the plasma so that the immiscible components are not present to alter or mask the characteristics to be observed.
In spite of the advent in recent years of many automatic and semiautomatic clinical chemistry analyzers, blood processing techniques have remained unchanged and time consuming. The present centrifugal separation technique commonly used for processing whole blood to serum or plasma (heparinized serum) requires the following steps:
1. collecting a whole blood sample in a test tube; PA1 2. removing the stopper from the test tube; PA1 3. rimming the specimen with a stirring rod; PA1 4. "balancing" the test tube (geometrically and symmetrically) in a centrifuge; PA1 5. centrifuging the test tube for 10 minutes at a relative centrifugal force (RCF) of 850 to 1,000; PA1 6. decanting or aspirating the serum into a serum container; and PA1 7. transporting the serum to an analyzer station.
While this technique is commonly used to process blood samples, it requires approximately 30 minutes to process a single sample. Thus, this technique is ill-suited for use in modern automated laboratories capable of analyzing up to 120 blood samples per hour.
"Batch" centrifuging has been utilized to process a plurality of blood samples simultaneously. However, successive batches may not contain the same number of samples, and accordingly, the centrifuge should be rebalanced after each batch to prevent vibrations which might damage the centrifuge. Moreover, the batch size (i.e., the number of samples in a batch) is limited because the plasma should be decanted or aspirated as soon as possible after the centrifuge is stopped, or the immiscible components will rediffuse into the plasma.
Accordingly, complex mechanical devices have been devised to automatically separate the serum or plasma from whole blood. However, the systems heretofore devised have generally been so mechanically complex and expensive that their use has been limited.